1. Field of the Invention
This invention relates generally to methods and apparatus for treating a fluidizable solid, such as natural and artificial sludges, having one or more polychlorinated biphenyls absorbed or adsorbed thereon, leaving a relatively uncontaminated solid material. More particularly, the present invention is directed to processes and apparatus for separation of polychlorinated biphenyls from a fluidizable solid material so that the fluidizable solids can be returned to this source or otherwise used as non-hazardous materials. The separated polychlorinated biphenyls, in relatively concentrated form, are easily disposed of, such as by burial or incineration.
2. Background and Prior Art
Polychlorinated biphenyls, or PCBs, were manufactured from 1929 to 1978. The manufacture of polychlorinated biphenyls has been banned in the United States since 1978. These chemicals have been widely used in capacitors, transformers, carbonless carbon paper, hydraulic pumps, vacuum pumps, heat transfer fluids, plasticizers, lubricants, caulking compounds, inks, paints and insect sprays. The major application of PCBs has been in large electrical capacitors and transformers. It has been estimated that over 800 million pounds of PCBs have been produced. A tremendous amount of these chemicals, suspected of causing cancer and birth defects, have been dumped over a number of years, either accidentally or deliberately, in an entirely reckless fashion. Commonly, these chemicals were dumped in lakes, streams and waterways where they eventually collected in the bottom material in considerable concentrations.
The accumulation of PCBs in human and animal tissue and their toxic effects have been well documented. Further, PCBs are a significant hazard to the environment and their disposal has caused great concern. Incineration and land burial have been the main methods of PCB disposal. However, while incineration has been demonstrated effective for liquid contaminaed PCBs, incineration of solid wastes containing PCBs has not ben demonstrated (Federal Register, Vol. 41, No. 64, Apr. 1, 1976). Accordingly, solids containing PCBs, such as waterway sludge, had to be buried in a chemical waste landfill. The great volume of sludge for transportation and burial represents a tremendous cost for such PCB disposal.
Because of the method of dumping toxic chemicals such as PCBs, tremendous mass of soil has been contaminated. In the past, bottom soils or the like contaminated with these toxic organic fluids have been treated by attempting to burn or by burning them. Because of the nature of the materials in which the PCB contamination is often found, burning is extremely difficult and burying is often only a stop gap measure. Many microorganisms have been reported that can degrade PCBs to some degree. The limited information presently available indicates that PCBs have a strong affinity for soil.
It has been recognized that thermal decomposition of polychlorinated organic compounds is possible despite the very high degree of thermal stability of these compounds. U.S. Pat. No. 4,140,066 discloses a method of decompositing PCBs by exposure to heat in a combustion chamber which operates with extremely intense turbulence and pulsation under temperatures as low as 850.degree. C. and with residence times as short as 0.1 second. However, the patent provides no method or apparatus for dealing with the problem of the treatment of mountainous amounts of contaminated, wet material having a relatively low heating value. Thus, while the method set forth in the U.S. Pat. No. 4,140,066 may be highly useful in eliminating PCB containing compounds in relatively small volumes, the process is not particularly helpful in dealing with contaminations on the order of tons in the form of residues in solids such as sludge.
A variety of techniques for incinerating waste materials are known. The following U.S. patents are exemplary: U.S. Pat. Nos. 4,245,570; 3,858,534; 3,829,558; 3,812,794; 3,716,339; and 3,511,194. A device such as the Williams U.S. Pat. No. 4,245,570 has been found to be effective in drying sewage sludge, but, prior to the present invention, has not been used to remove toxic chemicals from a fluidizable solid material, such as a sludge e.g., sand, clay, diatomaceous earth, charcoals, carbon, coals, silicas, alumina, silica-aluminas, metal particulates, metallic ores, and artificial sludges, such as those resulting from industrial spill absorption of liquids into an absorbent material.